Shinji YAMAGUCHI*
including installing sensors to monitor abnormal sediment flows, and send the information to the relevant organiza-tions to help establish warning and evacuation systems for the public.
To take appropriate measures to deal with volcanic eruptions, such as the implementation of structural works, it is necessary to know the types of volcanic phenomena and the extent of the damage. Volcanic hazard maps are produced as part of these efforts. They show the possible extent of the damage, as estimated by numerical simulations or other means, in the case of volcanoes that are expected to cause serious social and physical damage once they erupt. On the basis of these volcanic hazard maps, volcanic disaster prevention maps, which show evacuation sites and disaster-prevention information and describe eruption phenomena, are prepared by municipali-ties to promote public response and evacuation activimunicipali-ties (Fig. 1).
3. Sabo Plan for Urgent Measures for Volcanic Disaster Reduction
3.1 Outline of the Plan
It is difficult to fully prevent sediment-related disasters resulting from volcanic eruptions, even if appropriate measures—including the development of facilities—are systematically taken on the basis of volcanic sediment and erosion control plans. This is because it is difficult to determine the occurrence of volcanic eruption activity or its scale, which can become very large. Therefore, Sabo Plans for Urgent Measures for Volcanic Disaster Reduction (hereinafter “Volcano Disaster Sabo Plans”) are formulated by the sediment control personnel of the central and prefectural governments to minimize the damage caused by volcanoes that are highly likely to erupt and for which a high risk of sediment-related damage is associated with the volcanic eruption.
A Volcano Disaster Sabo Plan should be produced for each volcano that is expected to have serious social impacts if it erupts. As of 2012, twenty-nine volcanoes are the targets of this planning. The volcanoes are:
Technical Note of the National Research Institute for Earth Science and Disaster Prevention, No. 380 ; July, 2013
Fig. 1 (Top) Example of a volcano hazard map (results of a simulation of snowmelt-type volcanic mudfl ows on Fujisan).
(Bottom) Example of a volcanic disaster prevention map (for the city of Fujiyoshida).
Maximum flow depth (m)
Meakandake, Tokachidake, Tarumaesan, Usuzan, Hokkaido-Komagatake, Iwakisan, Yakeyama, Akita-Komagatake, Iwatesan, Chokaisan, Zaozan, Azumayama, Adatarayama, Bandaisan, Nasudake, Asamayama,
Kusatsu-Shiranesan, Izu-Oshima, Miyakejima, Niigata-Yakeyama, Yakedake, Ontakesan, Fujisan, Tsurumidake a n d G a r a n d a k e , K u j u s a n , . U n z e n d a k e , A s o s a n , Kirishimayama and Sakurajima
Actions for Volcanic Disaster Management — S. YAMAGUCHI
Fig. 2 Outline of the Sabo Plan for Urgent Measures for Volcanic Disaster Reduction.
Urgent hard works
Urgent installation of equipment to monitor volcanic activities
Assumption of danger zones by real time hazard mapping
Setting up the buffer zone at the foot of the volcano Establishment of
information communi-cation system using optical fiber cable etc.
Storage of emer-gency equipment and materials
Strengthening the function of the volcanic disaster prevention center Measures to be taken during
the non-disaster time Measures to be taken urgently at the time of eruption
3.2 Position of the Sabo Plan for Urgent Measures for Volcanic Disaster Reduction, and study system
Disaster-prevention measures should be implemented through the coordinated action of relevant organiza-tions, as they involve a variety of activities, including monitoring and observation of volcanic activity, provision of volcano-related information, protection of residents’
lives by promoting evacuation or setting restricted zones, and prevention or mitigation of damage to social assets or housing. Therefore, it is important to prepare a Volcano Disaster Sabo Plan through the coordination of measures from relevant organizations and of disaster-prevention plans from relevant municipalities. Given their importance, Volcano Disaster Sabo Plans are examined by a study group composed of members of relevant orga-nizations, including the Meteorological Agency, the Self Defense Forces, fire departments, and police; administra-tive agencies, including prefectures and municipalities;
and volcano specialists. The sediment-control sections of The Ministry of Land, infrastructure, Transport and Tourism’s Regional Development Bureaus and prefectural governments take the initiative.
3.3 Contents of the Sabo Plan for Urgent Measures for Volcanic Disaster Reduction
Designed to produce the maximum effect in case of emergency, a Volcano Disaster Sabo Plan consists of two sections, namely actions taken in emergency situations and actions taken in times of non-disaster to prepare for emergency situations. Emergency actions include emergency structural measures, such as reinforcement of sediment-control weirs or construction or improvement of sand pockets or training dikes, and emergency nonstruc-tural measures, such as urgent installation of equipment
to monitor volcanic activity or the assumption of danger zones through real-time hazard mapping. Preparatory actions include stockpiling of necessary materials and equipment, such as concrete block, or strengthening of the functions of volcanic disaster prevention centers (Fig. 2).
4. Emergency Survey Based on the Sediment Disasters Prevention Act
4.1 Outline of the Survey
Appropriate advice based on advanced technology is essential for a municipality to make an appropriate judgment on the evacuation of residents in a situation where a large-scale sediment-related disaster is imminent owing to, for example, a volcanic eruption. The Act for Partial Revision of the Act on Promotion of Sediment Disaster Countermeasures for Sediment Disaster Prone Areas (herein the “Revised Sediment Disasters Prevention Act”) was approved by the 176th Cabinet (Extraordinary Diet) on 17 November 2010. This revision specifies that the central government must conduct emergency surveys on the debris flows that could be caused by a volcanic eruption and notify relevant municipalities and the general public of the estimated extent and timing of the damage.
4.2 Case example: Emergency survey of the eruption of.
Kirishimayama (Shinmoedake)
Kirishimayama (Shinmoedake), which started erupting on 19 January 2011, had a full-scale magma eruption on the 26th of the same month and began explosive eruptions on the 27th.
The Kyushu Regional Development Bureau had its sediment control personnel survey the amount of fallen volcanic ash on 27 January. The survey team identified those mountain streams that satisfied the emergency
Technical Note of the National Research Institute for Earth Science and Disaster Prevention, No. 380 ; July, 2013
Fig. 3 Example of the status of emergency survey and sediment-related disaster emergency information.
Extent of area with ash falls over 1cm thick
Debris-flow torrent to moun-tain streams, as revealed by the emergency survey
Simulation of the area highly likely to be damaged by debris flows
survey requirements as those likely to be damaged by debris flows torrent and started an emergency survey ahead of the official enactment of the Revised Sediment Disasters Prevention Act. The emergency survey was conducted by the Bureau with technical support from the Public Works Research Institute. It included an analysis of the extent of the area highly likely to be damaged by the flood of debris flows. On the basis of data on the debris flows that occurred following the eruption of Miyakejima, the Bureau also proposed a criterion of an hourly rainfall of 4 mm as the trigger for a debris flow. Information on the
analyzed extent and timing was provided to Miyakonojyo City, Takaharu Town, and Miyazaki Prefecture as reference information to help issue evacuation advice to municipalities. With the official enactment of the Revised Sediment Disasters Prevention Act on 1 May, the survey was officially designated a regulatory emergency survey, and the emergency information on sediment-related disaster was then provided to the relevant municipali-ties. The rainfall criterion was revised on a timely basis by considering the actual rainfall data and the status of sediment movement (Fig. 3).
Technical Note of the National Research Institute for Earth Science and Disaster Prevention, No. 380 ; July, 2013
* Sabo and Landslide Technical Center